Papers by Manh-Linh Nguyen
PeerJ
The flathead gray mullet (Mugil cephalus L.) is a cosmopolitan fish that lives in warm and temper... more The flathead gray mullet (Mugil cephalus L.) is a cosmopolitan fish that lives in warm and temperate zones over 42°N–42°S. It is a key fish species for industrial fishing off coastal Taiwan. Gray mullets enter the coastal waters of the southeastern Taiwan Strait (22°N–25°N) to spawn in winter and feed in the coastal and tidal waters of China (25°N–30°N). From 1986 to 2010, the annual catch of gray mullet decreased substantially and remained low. Although the Pacific Decadal Oscillation and El Niño–Southern Oscillation are recognized to affect gray mullet migration, the increase in sea surface temperature may be the main cause of the aforementioned decrease. We explored how weather changes affect fishing conditions and patterns at the gray mullet fishing grounds in Taiwan’s coastal areas. Because of the decrease in gray mullet catches, the most common method for catching gray mullet in Taiwan’s coastal areas between 1990 and 2010 was the use of drift or trawl nets instead of two-boat...
PeerJ, 2023
The flathead gray mullet (Mugil cephalus L.) is a cosmopolitan fish that lives in warm and temper... more The flathead gray mullet (Mugil cephalus L.) is a cosmopolitan fish that lives in warm and temperate zones over 42 N-42 S. It is a key fish species for industrial fishing off coastal Taiwan. Gray mullets enter the coastal waters of the southeastern Taiwan Strait (22 N-25 N) to spawn in winter and feed in the coastal and tidal waters of China (25 N-30 N). From 1986 to 2010, the annual catch of gray mullet decreased substantially and remained low. Although the Pacific Decadal Oscillation and El Niño-Southern Oscillation are recognized to affect gray mullet migration, the increase in sea surface temperature may be the main cause of the aforementioned decrease. We explored how weather changes affect fishing conditions and patterns at the gray mullet fishing grounds in Taiwan's coastal areas. Because of the decrease in gray mullet catches, the most common method for catching gray mullet in Taiwan's coastal areas between 1990 and 2010 was the use of drift or trawl nets instead of two-boat purse-seiner fleets. Since 2012, purse-seiner fleets have become the most common method for catching gray mullet. This trend indicates that the local fishing industry is adapting to changing environmental conditions.
This study employed an arithmetic mean model with sea surface temperature and chlorophyll data (2... more This study employed an arithmetic mean model with sea surface temperature and chlorophyll data (2-month lag) to determine the projected impact of climate change on the immature albacore tuna habitat in the Indian Ocean. Albacore tuna fishing data from Taiwanese longline fishery from 2000 to 2016 were used. Standardization of the nominal catch per unit effort data was performed to prevent bias and overestimation resulting from various temporal and spatial factors. In the Indian Ocean, potential immature albacore habitats exhibited significant habitat suitability index (HSI) changes in response to future climate change levels. As the water stratifies in a projected warm climate, low HSI areas were enlarged, and potential immature albacore habitats exhibited a net southward shift. Although the CMIP5 climate model sea surface temperature projections generated different HSI patterns for immature albacore, our results from the ensemble median immature albacore habitat forecasts provided i...
Journal of the Fisheries Society of Taiwan, 2021
Swordtip squid (Uroteuthis edulis) is a commercial species and is obtained through inshore torch-... more Swordtip squid (Uroteuthis edulis) is a commercial species and is obtained through inshore torch-light fishery in the waters off Northeastern Taiwan. Using fishery data collected from 2015 and 2019, we analyzed the characteristics of the fishing ground as well as the spatial and temporal distributions of U. edulis to obtain a preliminarily understanding of resource utilization. The results indicated that the cumulative catch of swordtip squid accounts for 45% of the total cephalopod catch in this area, with the highest cumulative catch and highest monthly average catch-per-unit effort between April and October. In addition, based on the longitudinal and latitudinal gravity centers of the fishing ground, we concluded that in the first 3 months of the year, swordtip squid fishing is mainly concentrated in the area adjacent to Peng-Chia Yu Islet; the fishing ground then moves northeastward and to the waters off Peng-Chia Yu Islet. Lastly, the longitudinal and latitudinal frequency distribution showed that the traditional fishing area is adjacent to Peng-Chia Yu Islet. Further studies are needed to understand the environmental effects on spatial and temporal variations in swordtip squid distribution.
Journal of the Fisheries Society of Taiwan, 2021
The grey mullet (Mugil cephalus) is a commercial cosmopolitan fish species of the family Mugilida... more The grey mullet (Mugil cephalus) is a commercial cosmopolitan fish species of the family Mugilidae and is mainly distributed in the southwestern and northeastern coastal waters of Taiwan. In this study, using satellite images and data from the 2015-2018 grey mullet fishery, we examined variations in the spatial and temporal distribution of grey mullets and the effects of climate change on their distribution in the Taiwan Strait. The results revealed a decreasing trend in the temperature from 24°C in November to 18 °C in February and the migration of the 20 °C isotherms to the north of approximately 23 °N from 2001 to 2020, resulting in high grey mullet catches occurring more frequently at higher latitudes. Furthermore, decreasing trends in grey mullet catches and fishermen populations have caused the main fishing method for grey mullet to change from purse seine to gillnet after the 1980s. Finally, it is suggested that the decrease in grey mullet catches is influenced by the warming effect of sea surface temperature in the Taiwan Strait.
Journal of the Fisheries Society of Taiwan, 2021
The moonfish (Mene maculata) is a common fish caught by inshore fisheries in the waters off south... more The moonfish (Mene maculata) is a common fish caught by inshore fisheries in the waters off southwestern Taiwan. Considering the sustainable utilization of fishery resources, the aims of this study are to analyze the characteristics of the temporal and spatial changes of moonfish catch location and to estimate the length-weight relationship on the moonfish. According to 2014-2016 fishery data, the primary fishing methods in this area are Taiwanese seine and trawl. Generally, moonfish is mainly caught by Taiwanese purse seine. Moonfish hotspots, located on the southwestern coast of Taiwan, produce a high catch per unit effort (CPUE). Over time, relatively distinct spatial variations have occurred in moonfish hotspots; most notably, numerous moonfish was caught in the waters offshore of Penghu in 2016. The most productive fishing season is from January to March, and the main fishing grounds are in coastal waters off southwestern Taiwan. From April to September, the fishing grounds are relatively far from the shore and somewhat scattered. By analyzing 388 moonfish samples collected from the southwestern waters of Taiwan, it indicates that positive allometric growth (b > 3) for moonfish, indicating fish grew faster in weight than in length, and the good correlation between body length and body weight. Further studies are recommended to explore the relationship between environmental factors the spatio-temporal distribution of moonfish as well as the affecting factors of the L-W relationship.
Journal of the Fisheries Society of Taiwan, 2021
Swordtip squid (Uroteuthis edulis) is a commercial species and is obtained through inshore torch-... more Swordtip squid (Uroteuthis edulis) is a commercial species and is obtained through inshore torch-light fishery in the waters off Northeastern Taiwan. Using fishery data collected from 2015 and 2019, we analyzed the characteristics of the fishing ground as well as the spatial and temporal distributions of U. edulis to obtain a preliminarily understanding of resource utilization. The results indicated that the cumulative catch of swordtip squid accounts for 45% of the total cephalopod catch in this area, with the highest cumulative catch and highest monthly average catch-per-unit effort between April and October. In addition, based on the longitudinal and latitudinal gravity centers of the fishing ground, we concluded that in the first 3 months of the year, swordtip squid fishing is mainly concentrated in the area adjacent to Peng-Chia Yu Islet; the fishing ground then moves northeastward and to the waters off Peng-Chia Yu Islet. Lastly, the longitudinal and latitudinal frequency distribution showed that the traditional fishing area is adjacent to Peng-Chia Yu Islet. Further studies are needed to understand the environmental effects on spatial and temporal variations in swordtip squid distribution.
Vietnam Journals of Earth Sciences, 2011
A palynological study of two sediment cores from the Hanoi area shows the climate change and huma... more A palynological study of two sediment cores from the Hanoi area shows the climate change and human impact in the Early and Middle Holocene. The abundance of tropical and subtropical vegetation in the period 10.5 to 5.8 Kcal years BP shows a humid and hot climate in the Hanoi area. However, there is a short time of cold and dry climate between 8.2 - 8.4 Kcal years BP. After 6.5 Kcal years ago, the diversity and abundance of tropical and subtropical vegetation show a high rainfall and hot climate. The starting of human activities to be identified in this area at about 6000 years ago, imprinted by the higher values of Graminae and Alnus in both 2 cores.
Conference Presentations by Manh-Linh Nguyen
Conference on the Fisheries Society of Taiwan, 2023
This study collected the Taiwanese seine fisheries data in the Linyuan area, Kaohsiung City, betw... more This study collected the Taiwanese seine fisheries data in the Linyuan area, Kaohsiung City, between 2013 and 2021, aiming to discuss the fish compositions and their spatial and temporal variations. Moreover, this study analyzed 1210 biological samples collected from this area from 2021 to 2022. Our results show that in the fish composition, moonfish (Mene maculata) was the predominant species caught by Taiwanese seine in the study area, accounting for approximately 41.5%. Regarding the biological analysis results, they indicate that the L–W relationship of moonfish in this study was illustrated as the following: BW=0.00003FL2.9579 (in 2021) and BW=0.00003FL2.886 (in 2022), demonstrating the hypo-allometric growth for moonfish. Furthermore, the frequency distribution of fork lengths and body weights suggests that moonfish may spawn in summer and autumn, and the stock may grow and recruit in spring and winter. The following studies will discuss the relationship between local oceanographic variables and the catches of the target species.
Conference on Fisheries Society of Taiwan, 2023
To examine variation in the catches of moonfish and to discuss their spatial-temporal distributio... more To examine variation in the catches of moonfish and to discuss their spatial-temporal distribution in the waters off southwestern Taiwan, this study collected fishery data as Voyage Data Recorder (VDR) and records from fishing harbors between 2013 and 2021. The analysis results indicated that the Taiwanese seine was the main fishing method for catching moonfish, and its moonfish catch accounted for approximately 99% and was followed by that of the trawl. Regarding the monthly moonfish catches and average CPUE, the highest was in March, followed by three months consisting of March, February, and December; as a subsequence, it indicated they had seasonal variation. Furthermore, we also concluded that the main moonfish fishing grounds were near Kaohsiung City, in which the Linyuan area was the place having the highest moonfish catches. This study also showed that the longitudinal and latitudinal gravity centers and fishing locations of the moonfish fishery in the waters of southwestern Taiwan would change with the lapse of time. The result of the Generalized Addictive Models (GAM) analysis pointed out that variation in the moonfish spatial distribution was mainly caused by sea-surface temperature, and sea-surface height, and slightly affected by other environmental factors: salinity, chlorophyll-a concentration, and mixed-layer depth. Furthermore, it is clear to identify that the higher moonfish CPUE was between January and March when all environmental factors were suitable for the target species. In the further research, we will focus on the development of habitat modelling and its application to fisheries management.
International Conference on Earth Observation and Societal Impact , 2021
The swordtip squid (Uroteuthis edulis) is a cosmopolitan species distributed between 40oN and 40o... more The swordtip squid (Uroteuthis edulis) is a cosmopolitan species distributed between 40oN and 40oS (Jereb and Roper, 2010) and in the depth of 30 to 170m of tropical and subtropical areas. Also, it is one of the most important commercial species for the torchlight fishery in northeastern Taiwan. This study aims to investigate the distribution of this species about the oceanic environment and its applicability to modeling habitat in northeast Taiwan.
In this study, Swordtip squid fishery data, simultaneously collected during the period between 2014 and 2019, includes fishing time (date, month, year), fishing position (longitude and latitude), fishing effort, and catchweight (kg). Remote sensing environment data was exacted from the Hybrid Coordinate Ocean Model (HYCOM) of the National Oceanic and Atmospheric Administration (NOAA) in comparison to Ocean Circulation Models (OCM) of Taiwan Central Weather Bureau with a spatial resolution of 1.1km.
Our study indicates that several oceanic environmental factors such as sea-water temperature (SST), sea-water salinity (SSS), chlorophyll-a concentration (SSC), sea-surface height (SSH), current play vital keys in a variation of the object’s distribution. The analysis of Habitat Suitability Indices (HSI) reveals that the Chlorophyl-a factor influences variation of swordtip squid CPUE. Also, the optimal range of hydrological variables in SST, SSC, SSS, SSH, MLD, and current for the habitat of Squid was 25-28°C, 0.09-1.0 mg m-3, 33.5-34.5 psu, 0.5-0.7 m, 10-20 m, and 0.2-0.4 m/s, respectively. Finally, we could conclude that Swordtip squid’s habitat modeling is valuable for predicting potential fishing grounds and ecosystem-based fishery management.
Keywords: Swordtip squid, Habitat Modelling, Northeastern Taiwan, Habitat Suitability Indices (HSI), Potential fishing zones.
Books by Manh-Linh Nguyen
農漁業健康環境形塑, 2022
年劍尖槍鎖管的漁獲量為例，其月別平均漁獲量可達380,000 公斤/ 月，平均「單位努力漁獲量」（catch per unit effort, CPUE）可達24 公斤/ 小時。冬末春初時劍尖槍... more 年劍尖槍鎖管的漁獲量為例，其月別平均漁獲量可達380,000 公斤/ 月，平均「單位努力漁獲量」（catch per unit effort, CPUE）可達24 公斤/ 小時。冬末春初時劍尖槍鎖管的漁獲重心主要分布在彭佳嶼附近，之後逐漸往東北方移動至東經124 度暨北緯27 度附近水域；夏秋季時逐漸往西側陸棚水域和南側水域移動，到冬季時再回到彭佳嶼附近海域。根據「泛加成模式」（generalized additive model, GAM）和「算術平均棲地模式」（arithmetic mean model, AMM）的分析結果，劍尖槍鎖管棲地的最適環境條件是葉綠素濃度範圍在0.47mg/m3-0.64mg/m3、海表溫度範圍介於27.7℃ -28.7℃、而海表鹽度落在33.8psu-34.4psu 之間的水域。
湧升流的形成是由於風或地形變化所導致的由下往上的海流，同時帶來豐富的營養鹽。湧升流的形成會使水體的垂直結構改變，使混合層深度變淺，甚至消失。全球有許多湧升流區，主要分布在陸棚區域。臺灣周邊的湧升流區有三個，分別是臺灣灘、澎湖和臺灣東北部。其中，臺灣灘與澎湖湧升流為南海海流進入臺灣海峽之後受地形影響而形成的，臺灣東北部的湧升流則為黑潮入侵流形成之渦流而產生。為了預測湧升流的發生，我們透過水平湧升流指標與垂直混合層深度的判定機制來預測湧升流，進行加權之後得到預報結果。將預報結果與葉綠素濃度分析做比對，湧升流出現機率高的區域與葉綠素濃度分布的區域大致相符合，但其結果仍因採取的模式不同而有差異。
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Papers by Manh-Linh Nguyen
Conference Presentations by Manh-Linh Nguyen
In this study, Swordtip squid fishery data, simultaneously collected during the period between 2014 and 2019, includes fishing time (date, month, year), fishing position (longitude and latitude), fishing effort, and catchweight (kg). Remote sensing environment data was exacted from the Hybrid Coordinate Ocean Model (HYCOM) of the National Oceanic and Atmospheric Administration (NOAA) in comparison to Ocean Circulation Models (OCM) of Taiwan Central Weather Bureau with a spatial resolution of 1.1km.
Our study indicates that several oceanic environmental factors such as sea-water temperature (SST), sea-water salinity (SSS), chlorophyll-a concentration (SSC), sea-surface height (SSH), current play vital keys in a variation of the object’s distribution. The analysis of Habitat Suitability Indices (HSI) reveals that the Chlorophyl-a factor influences variation of swordtip squid CPUE. Also, the optimal range of hydrological variables in SST, SSC, SSS, SSH, MLD, and current for the habitat of Squid was 25-28°C, 0.09-1.0 mg m-3, 33.5-34.5 psu, 0.5-0.7 m, 10-20 m, and 0.2-0.4 m/s, respectively. Finally, we could conclude that Swordtip squid’s habitat modeling is valuable for predicting potential fishing grounds and ecosystem-based fishery management.
Keywords: Swordtip squid, Habitat Modelling, Northeastern Taiwan, Habitat Suitability Indices (HSI), Potential fishing zones.
Books by Manh-Linh Nguyen
湧升流的形成是由於風或地形變化所導致的由下往上的海流，同時帶來豐富的營養鹽。湧升流的形成會使水體的垂直結構改變，使混合層深度變淺，甚至消失。全球有許多湧升流區，主要分布在陸棚區域。臺灣周邊的湧升流區有三個，分別是臺灣灘、澎湖和臺灣東北部。其中，臺灣灘與澎湖湧升流為南海海流進入臺灣海峽之後受地形影響而形成的，臺灣東北部的湧升流則為黑潮入侵流形成之渦流而產生。為了預測湧升流的發生，我們透過水平湧升流指標與垂直混合層深度的判定機制來預測湧升流，進行加權之後得到預報結果。將預報結果與葉綠素濃度分析做比對，湧升流出現機率高的區域與葉綠素濃度分布的區域大致相符合，但其結果仍因採取的模式不同而有差異。
In this study, Swordtip squid fishery data, simultaneously collected during the period between 2014 and 2019, includes fishing time (date, month, year), fishing position (longitude and latitude), fishing effort, and catchweight (kg). Remote sensing environment data was exacted from the Hybrid Coordinate Ocean Model (HYCOM) of the National Oceanic and Atmospheric Administration (NOAA) in comparison to Ocean Circulation Models (OCM) of Taiwan Central Weather Bureau with a spatial resolution of 1.1km.
Our study indicates that several oceanic environmental factors such as sea-water temperature (SST), sea-water salinity (SSS), chlorophyll-a concentration (SSC), sea-surface height (SSH), current play vital keys in a variation of the object’s distribution. The analysis of Habitat Suitability Indices (HSI) reveals that the Chlorophyl-a factor influences variation of swordtip squid CPUE. Also, the optimal range of hydrological variables in SST, SSC, SSS, SSH, MLD, and current for the habitat of Squid was 25-28°C, 0.09-1.0 mg m-3, 33.5-34.5 psu, 0.5-0.7 m, 10-20 m, and 0.2-0.4 m/s, respectively. Finally, we could conclude that Swordtip squid’s habitat modeling is valuable for predicting potential fishing grounds and ecosystem-based fishery management.
Keywords: Swordtip squid, Habitat Modelling, Northeastern Taiwan, Habitat Suitability Indices (HSI), Potential fishing zones.
湧升流的形成是由於風或地形變化所導致的由下往上的海流，同時帶來豐富的營養鹽。湧升流的形成會使水體的垂直結構改變，使混合層深度變淺，甚至消失。全球有許多湧升流區，主要分布在陸棚區域。臺灣周邊的湧升流區有三個，分別是臺灣灘、澎湖和臺灣東北部。其中，臺灣灘與澎湖湧升流為南海海流進入臺灣海峽之後受地形影響而形成的，臺灣東北部的湧升流則為黑潮入侵流形成之渦流而產生。為了預測湧升流的發生，我們透過水平湧升流指標與垂直混合層深度的判定機制來預測湧升流，進行加權之後得到預報結果。將預報結果與葉綠素濃度分析做比對，湧升流出現機率高的區域與葉綠素濃度分布的區域大致相符合，但其結果仍因採取的模式不同而有差異。